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Stock-Based Compensation Stock-Based Compensation (Schedule of Restricted Stock Awards and Stock Options) (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Abstract]        
Recognized stock compensation expense $ 1.9 $ 2.1 $ 7.2 $ 11.2
Capitalized stock compensation cost for our oil and natural gas properties 0.4 0.7 1.6 2.6
Tax benefit on stock based compensation $ 0.7 $ 0.8 $ 2.7 $ 4.2